Administration of hypocholesterolemic drugs, AY9944 or Triparanol, produced numerous intracytoplasmic inclusions in neurons, glial cells and endothelial cells in the brain as well as in the various cells of other organs in the rats. In the young rats, additional oligodendroglial changes were noted in the myelinating white matter. The inclusions similar to those found in the cells of these hypocholesterolemic-drug-treated animals were also reported in the animals treated with chloroquine, chlorphentermine, and chlorpromagine. To determine the oligodendroglial changes are specific reaction to the hypocholesterolemic drugs or simply age related general toxic response, these drugs will be administered to the animals using the same experimental protocols used for the hypocholesterolemic drugs. Alteration of lysosomal enzymes during the process of formation and regression of these inclusions will be also studied.